My neighbor just went to a NBS 07 CCSB Denali w/6.2/6spd from a ECSB Denali AWS and said his mileage is worse around town but up 2mpg highway.
Sweet truck BTW.

 

I thought the 6 speed trans were controlled by a separate BCM and could not be changed at this time. Anyway, the tow haul mode limits the trans to 5th gear for towing. If his is not shifting into 5th, have him take it back to the dealer.

 

they are on a sperate TCM, just like most of the trannies in all GM's now. Buy you can still tune them like always.

 

I have been messing with mine some. I've disabled the TM and raised the shift mph's and rpms's. This is a clutch to clutch tranny...not the same as the previous 4l60e and 4l80e's. I'm pretty much HPT stupid at this point, so I am not changing a whole lot until there is more info out on these things.

I have been told that if the 2 clutches do not sync properly, you can blow the tranny. Good luck with this and post up any info that you might find